Electron beam plasma source with profiled chamber wall for uniform plasma generation

ABSTRACT

A plasma reactor that generates plasma in a workplace processing chamber by an electron beam, has an electron beam source chamber with a wall opposite to the electron beam propagation direction, the wall being profiled to compensate for a non-uniformity in electron beam density distribution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 61/549,355, filed Oct. 20, 2011 entitled ELECTRON BEAM PLASMA SOURCE WITH PROFILED CHAMBER WALL FOR UNIFORM PLASMA GENERATION, by Kalloi Bera, et al.

BACKGROUND

A plasma reactor for processing a workplace can employ an electron beam as a plasma source. Such a plasma reactor can exhibit non-uniform distribution of processing results (e.g., distribution of etch rate across the surface of a workpiece) doe to non-uniform density distribution of the electron beam. Such non-uniformities can be distributed in a direction transverse to the beam propagation direction.

SUMMARY

A plasma reactor for processing a workpiece, includes a workpiece processing chamber having a processing chamber including a chamber ceiling and a chamber side wall and an electron beam opening in the chamber side wall, a workpiece support pedestal in the processing chamber having a workpiece support surface facing the chamber ceiling and defining a workpiece processing region between the workpiece support surface and the chamber ceiling, the electron beam opening facing the workpiece processing region. The plasma reactor further includes an electron beam source chamber including a source enclosure, the source enclosure having an electron beam emission window that is open to the electron beam opening of the workpiece processing chamber, and defining an electron beam propagation path along a longitudinal direction extending through the electron beam emission window and through the electron beam opening and into the workpiece processing region, the source enclosure further including a back wall displaced from the electron beam emission window by a gap along the longitudinal direction, the electron beam emission window extending generally along a direction transverse to the longitudinal direction. An electron beam extraction grid extends across the electron beam emission window. An extraction voltage source is coupled to the electron beam extraction grid, and a supply of plasma source power is coupled to the electron beam source chamber. The back wall has a profile corresponding to a variance in the gap along the transverse direction. In one embodiment, the profile is selected to be complementary to a variance in electron beam density along the transverse direction. In a related embodiment, the variance in the gap corresponds to a measured variance in electron beam density distribution along the transverse direction. The profile may be actively configurable. For example, the back wall may consist of plural slats that are removably inserted into the source enclosure through a. particular selection of various slots. Each profile corresponds to a different selection of the slots. As another example, the back wall may be a flexible sheet that can be deformed to different curvatures.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the exemplary embodiments of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be appreciated that certain well known processes are not discussed herein in order to not obscure the invention.

FIG. 1A is a side view of a plasma reactor having an electron beam generator as a plasma source, and having a beam dump that is profiled electrically or structurally.

FIG. 1B is an enlarged view of a portion of FIG. 1A.

FIG. 1C is a top view of the plasma reactor of FIG. 1A, in which a plasma source chamber wall has a convex profile.

FIG. 1D is a top view of the plasma reactor of FIG. 1A, in which a plasma source chamber wall has a concave profile.

FIGS. 2A and 2B depict different aspects of an embodiment in which profiling is implemented in a stepped configuration.

FIG. 3 depicts an embodiment which is transformable between different profiles, using insertable partitions.

FIGS. 3A, 3B and 3C depict different configurations of the embodiment of FIG. 3.

FIG. 3D is a detailed view of a portion of the embodiment of FIG. 3.

FIG. 4 depicts an embodiment which is transformable between different profiles, using a flexible chamber wall.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

DETAILED DESCRIPTION

Referring to FIGS. 1A, 1B and 1C, a plasma reactor has an electron beam plasma source. The reactor includes a process chamber 100 enclosed by a cylindrical side wall 102, a floor 104 and a ceiling 106. A workpiece support pedestal 108 supports a workplace 110, such as a semiconductor wafer, the pedestal 108 being movable in the axial (e.g., vertical) direction. A gas distribution plate 112 is integrated with or mounted on the ceiling 106, and receives process gas from a process gas supply 114. A vacuum pump 116 evacuates the chamber through the floor 104. A process region 118 is defined between the workpiece 110 and the gas distribution plate 112. Within the process region 118, the process gas is ionized to produce a plasma for processing of the workpiece 110.

The plasma is generated in process region 118 by an electron beam from an electron beam source 120. The electron beam source 120 includes a plasma generation chamber 122 outside of the process chamber 100 and having a conductive enclosure 124. The conductive enclosure 124 includes side wails 124 b, a ceiling 124 c, a floor 124 d and a back wall 124 e. The conductive enclosure 124 has a gas inlet or neck 125. An electron beam source gas supply 127 is coupled to the gas inlet 125. The conductive enclosure 124 has an opening 124 a facing the process region 118 through an opening 102 a in the sidewall 102 of the process chamber 100.

The electron beam source 120 includes an extraction grid 126 between the opening 124 a and the plasma generation chamber 122, and an acceleration grid 128 between the extraction grid 126 and the process region 118, best seen in the enlarged view of FIG. 1B. The extraction grid 126 and the acceleration grid 128 may be formed as separate conductive meshes, for example. The extraction grid 126 and the acceleration grid 128 are mounted with insulators 130, 132, respectively, so as to be electrically insulated from one another and from the conductive enclosure 124. However, the acceleration grid 128 is in electrical contact with the side wall 102 of the chamber 100. The openings 124 a and 102 a and the extraction and acceleration grids 126, 128 can be mutually congruent, generally, and define a thin wide beam flow path for an electron beam into the processing region 118. The width of the flow path is about the diameter of the workpiece 110 (e.g., 100-500 mm) while the height of the flow path is less than approximately two inches.

The electron beam source 120 further includes a pair of electromagnets 134-1 and 134-2 adjacent opposite sides of the chamber 100, the electromagnet 134-1 surrounding the electron beam source 120. The electromagnets 134-1 and 134-2 produce a magnetic field parallel to the direction of the electron beam along an electron beam path. The electron beam flows across the processing region 118 over the workpiece 110, and is absorbed on the opposite side of the processing region 118 by a beam dump 136. The beam dump 136 is a conductive body having a shape adapted to capture the wide thin electron beam.

A plasma D.C. discharge voltage supply 140 is coupled to the conductive cathode enclosure 124, and provides extraction voltage between cathode 124 and extraction grid 126. One terminal of an electron beam acceleration voltage supply 142 is connected to the extraction grid 126 and the other terminal to the acceleration grid 128 through the ground potential of the sidewall 102 of the process chamber 100. A coil current supply 146 is coupled to the electromagnets 134-1 and 134-2. Plasma is generated within the chamber 122 of the electron beam source 120 by a D.C. gas discharge produced by power from the voltage supply 140, to produce a plasma throughout the chamber 122. This D.C. gas discharge is the plasma source of the electron beam source 120. Electrons are extracted from the plasma in the chamber 122 through the extraction grid 126, and accelerated through the acceleration grid 128 due to a voltage difference between the acceleration grid and the extraction grid to produce an electron beam that flows into the processing chamber 100.

The distribution of electron density across the width of the beam (along the X-axis or direction transverse to beam travel) affects the uniformity of plasma density distribution in the processing region 118. The electron beam may have a measured non-uniform distribution, in the absence of features that correct such non-uniformities, which features are described below. Such non-uniformity may be measured from etch depth distribution measured on a workpiece or wafer processing in the reactor chamber described above. Such measured non-uniformity may be caused by electron drift due to the interaction of the bias electric field with the magnetic field, divergence of electron beam due to self electric field and/or electron collision with neutral gas in the process chamber. Such non-uniformity may also be caused by fringing of an electric field at the edge of the electron beam. The distribution of electron density across the width of the beam (across the X-axis or direction transverse to beam travel) is liable to exhibit non-uniformities due to the foregoing causes. Such non-uniformities may correspond to a variance in plasma electron density distribution in the electron beam across the width of the electron beam in a range of 1% to 20%, for example. Such a variance may be measured in that it may be inferred from the measurements of etch depth distribution in a test wafer referred to above.

The back wall 124 e of the conductive enclosure 124 is profiled along the transverse direction (X-axis). The profiling is chosen to compensate for a measured non-uniformity along the transverse direction in electron density distribution of the electron beam. For example, in the embodiment of FIG. 1C, the back wall 124 e is profiled in an internally convex shape, in which the back wall 124 e curves inwardly in the volume of the chamber 122 near the center and curves outwardly toward the side wails 124 b. The back wall 124 e and the opening 124 a define a gap G parallel to the beam direction or Y-axis, the gap G having a variance along the transverse direction or X-axis in accordance with the profile of the back wall 124 e.

In the embodiment of FIG. 1D, the back wall 124 e is profiled in an internally concave shape, in which the back wall 124 e curves outwardly relative to the volume of the chamber 122 near the center and curves inwardly toward the side walls 124 b.

It is believed that such profiling changes the effective cathode area along the transverse direction, which changes the distribution of ion current to the cathode (i.e., the conductive envelope 124) along the transverse direction. This creates a corresponding change in distribution along the transverse direction of electron current through the extraction grid 126. For example, a constriction in volume reduces plasma electron density. Thus, in the embodiment of FIG. 1C, the convex shape of the back wall 124 e tends to render plasma electron distribution along the transverse direction center low and edge high, and is therefore suitable when the uncorrected distribution is center high. In the embodiment of FIG. 1D, the concave shape of the back wall 124 e tends to render plasma electron distribution along the transverse direction center high and edge low, and is therefore suitable when the uncorrected distribution is center low. The variance of the gap G is chosen to match the variance in plasma electron density distribution along the transverse direction. For example, if the plasma electron distribution has a center-high non-uniformity or variance of a particular value (e.g., 5%), then the convex shape of FIG. 1C is employed, and the profile of the back wall 124 e in such a case is configured so that the gap G has a variance of a similar value (e.g., 5%), Similarly, if the plasma electron distribution has a center-low non-uniformity or variance of a particular value (e.g., 5%), then the concave shape of FIG. 1D is employed, and the profile of the back wall 124 e in such a case is configured so that the gap G has a variance of a similar value (e.g., 5%). The electron density distribution may have a variance in a range from 1% to 20%, for example, and the variance in the gap G may be chosen within this range.

FIGS. 2A and 28 depict embodiments in which the

profiling of FIGS. 1C and 1D, respectively, is implemented in a stepped manner.

FIG. 3 depicts an embodiment that may be transformed between different stepped configurations, including the stepped configurations of FIGS. 2A and 2B. In FIG. 3A, elongate slots 200 in the ceiling 124 c extend along respective directions. Individual slats or flat partitions 210 may be inserted into respective slots 200. The individual partitions 210 are slidable into and out from individual slots 200 until their bottom edges contact the floor 124 d, and may therefore be individually inserted or removed from the enclosure 124. Individual partitions 210 are inserted into selected ones of the slots 200 to form a contiguous conductive barrier consisting of the inserted partitions 210. This barrier may conform with either the convex or concave stepped profile of FIG. 2A or 2B, for example, or any other suitable profile. For each stepped configuration, some of the slots 200 have no partitions inserted into them and are therefore empty. Each slot 200 that is empty may be sealed with a slot cover 230 depicted in FIG. 3D.

FIGS. 3A through 3C depict different configurations of the partitions 210 of FIG. 3. The partitions 210 are indicated by cross-hatching, to distinguish them from empty slots 200. FIGS. 3A and 3B depict configurations corresponding to concave and convex profiles, respectively. FIG. 3C depicts a configuration having an almost fiat profile. FIG. 3D is an enlarged view illustrating certain details in accordance with related embodiments. Specifically, FIG. 3D illustrates how an individual slot cover 230 may be used to close unused slots 200. A number of slot covers 230 may be furnished to accommodate many possible configurations. In FIG. 3D, a shallow trough 124 f is provided in the surface of the floor 124 d, each trough 124 f being in registration with a corresponding slot 200 in the ceiling 124 c, and functioning to guide and hold in place the bottom edge of each partition 210 inserted into a slot 200. In order to provide a sealed enclosure, the top of each partition 210 and each slot cover 230 is provided with a lip 225 as depicted in FIG. 3D, and a deformable ring seal is provided under the lip.

FIG. 4 depicts an embodiment in which the back wall 124 e is a flexible metal sheet fastened at its side edges 124 e-1, 124 e-2 to the side walls 124 b. Top and bottom edges of the back wall 124 e are free to slide against the ceiling 124 c and floor 124 a. Thus, the back wall 124 e is free to flex between the convex curved shape of FIG. 1C and the concave curved shape of FIG. 1D. An actuator 250 is linked by an arm 255 to the back wall 124 e, and thereby flexes the back wall 124 e to the convex or concave profiles, under user control.

While the main plasma source in the electron beam source 120 is a D.C. gas discharge produced by the voltage supply 140, any other suitable plasma, source may be employed instead as the main plasma source. For example, the main plasma source of the electron beam source 120 may be a toroidal RF plasma source, a capacitively coupled RF plasma source, or an inductively coupled RF plasma source.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

What is claimed is:
 1. A plasma reactor for processing a workpiece, comprising: a workpiece processing chamber having a processing chamber comprising a chamber ceiling and a chamber side wall and an electron beam opening in said chamber side wall, a workpiece support pedestal in said processing chamber having a workpiece support surface facing said chamber ceiling and defining a workpiece processing region between said workpiece support surface and said chamber ceiling, said electron beam opening facing said workpiece processing region; an electron beam, source chamber comprising a source enclosure, said source enclosure having an electron beam emission window that is open to said electron beam opening of said workpiece processing chamber, and defining an electron beam propagation path along a longitudinal direction extending through said electron beam emission window and through said electron beam opening and into said workpiece processing region, said source enclosure further comprising a back wall displaced from said electron beam emission window by a gap along said longitudinal direction, said electron beam emission window extending generally along a direction transverse to said longitudinal direction; an electron beam extraction grid, across said electron beam emission window, an extraction voltage source coupled to said electron beam extraction grid, and the said electron beam source chamber; and said back wall having a profile corresponding to a distribution of said gap along said transverse direction.
 2. The plasma reactor of claim 1 wherein said distribution of said gap corresponds to a distribution in electron beam density along said transverse direction.
 3. The plasma reactor of claim 1 wherein said distribution of said gap along said transverse direction corresponds to a measured distribution in electron beam density distribution along said transverse direction.
 4. The plasma reactor of claim 1 wherein said distribution of said gap along said transverse direction is center-low, wherein said gap has a minimum value at a center location of said back wall along said transverse direction.
 5. The plasma reactor of claim 4 wherein said distribution of said gap along said transverse direction of said electron beam source chamber compensates for a measured distribution of plasma density along said transverse direction that is center-high.
 6. The plasma reactor of claim 1 wherein said distribution of said gap along said transverse direction is center-high, wherein said gap has a maximum value at a center location of said back wall along said transverse direction.
 7. The plasma reactor of claim 6 wherein said distribution of said gap along said transverse direction of said electron beam source chamber compensates for a measured distribution of plasma, density distribution along said transverse direction that is center-low.
 8. The plasma reactor of claim 1 wherein said, distribution of said gap along said transverse direction has a variance of least 1%.
 9. The plasma reactor of claim 1 wherein said distribution of said gap along said transverse direction has a variance of at least 5%.
 10. The plasma reactor of claim 1 wherein back wall is configurable for changing said profile.
 11. The plasma reactor of claim 1 wherein said back wall comprises a flexible member capable of deforming between different curvatures, and an actuator coupled to said flexible member.
 12. The plasma reactor of claim 11 wherein said different curvatures comprise a curvature corresponding to a concave profile or a curvature corresponding to a convex profile.
 13. The plasma reactor of claim 1 wherein said source enclosure further comprises a ceiling, a floor facing said ceiling, plural elongate slots in one of said floor and ceiling, said slots spaced apart from one another and at least some of said slots extending in different directions relative to said transverse and longitudinal directions, and plural slats removably inserted into selected ones of said slots to form respective barriers extending from said floor to said ceiling and through the selected, slots, said back wall comprising the slats inserted through said slots.
 14. The plasma reactor of claim 13 wherein said selected slots comprises a set of said plural slots corresponding to one of plural profiles.
 15. The plasma reactor of claim 14 wherein said plural profiles comprise a convex profile or a concave profile.
 16. The plasma reactor of claim 14 wherein said plural profile corresponds to a measured distribution in electron beam density distribution along said transverse direction.
 17. The plasma reactor of claim 11 wherein said different curvatures comprise a curvature corresponding to a measured distribution in electron beam density distribution along said transverse direction.
 18. The plasma reactor of claim 1 further comprising: an electron beam acceleration grid or slot separated by a dielectric from the said electron beam extraction grid, an acceleration voltage source coupled to said electron beam acceleration grid or slot, and the said extraction grid. 